The nucleation and undercooling of Al4Mn alloy have been investigated with 1.2 meter long drop tube. Melt droplets were solidified in vacuum and various sizes of droplets were collected at the bottom of the tube. Besides orthorhombic Al6Mn and β-Mn phases, there are two approximants of the decagonal quasicrystal, one approximant of the icosahedral quasicrystal, and decagonal domains, observed in the droplets. However, the amount of each phase is different in samples of various sizes due to the different cooling rates and undercooling. The relationship between the phase composition and the sample size was discussed on the basis of the classical nucleation and growth theories.